Today, many dyes are known and they are broadly classified into natural dyes and synthetic dyes. Examples of the synthetic dyes include aniline blue, fuchsine and methyl orange. Most of the synthetic dyes have an aromatic or heterocyclic ring, and they are each classified as either an ionic compound (e.g., all water-soluble dye) or a nonionic compound (e.g., disperse dye). In addition, in the case of ionic dyes, they are classified into anionic dyes and cationic dyes.
The cationic dyes are made of an organic cation, which has a positive charge delocalized over a covalent bond, and an anion, which is generally inorganic. Also, they are generally dyes in which an amino group, which can have a substituent group, is involved in resonance. Therefore, the selection of cationic dyes depends on the number and type of anions, which are counter ions. Examples of counter anions include chloride ion, bromide ion, iodide ion, perchlorate ion, tetrafluoroborate ion, hexafluorophosphate ion, alkyl or aryl sulfate ion, tosylate ion, acetate or oxalate ion, etc.
In general, rhodamine, safranine and victoria blue, which are cationic dyes, have a chloride ion or tosic acid as a counter ion. However, these compounds have insufficient heat resistance.
An example in which a chloride ion or an aryl sulfate ion is used as a counter anion of a triarylmethane dye to improve heat durability of the triarylmethane dye, is known (for example, see Patent Literature 1).
In Patent Literature 2, as a method of obtaining a color composition for color filters with excellent color characteristics, heat resistance, light resistance and solvent resistance, a salt-forming compound comprising a triarylmethane basic dye and a sulfonated organic compound having at least two sulfonic groups, is disclosed.
In Patent Literature 3, as a method of obtaining a coloring resin composition which has not only excellent light resistance but also excellent light resistance, a salt forming method has been reported, in which a salt is formed by using a sulfonated compound of a dye skeleton such as phthalocyanine or anthraquinone, which is the counter anion, in combination with a triarylmethane skeleton, which is the cation.
However, the salt-forming compounds of dyes and counter anions disclosed in Patent Literatures 1 to 3 have insufficient heat resistance and insufficient fiber dyeing property, so that they have a problem of loss of color.
A polysiloxane dye is disclosed in Patent Literature 4, which is highly cross-linked by polysiloxane containing at least ten Si atoms. However, due to its synthesis method, the polysiloxane dye disclosed in Patent Literature 4 is a mixture in which an unreacted compound having only one dye skeleton or dyes with different polymerization degrees are present. Therefore, the physical properties of the dye are not stable, such as the case where, like the below-described Comparative Examples, while part of the polysiloxane dye is not dissolved in solvent, fibers dyed with the dye causes partial loss of color by washing. Also, it is difficult to separate only a dye with a specific polymerization degree from the polysiloxane dye, so that there is a problem with the productivity of the polysiloxane dye.